Biology

The direct result of the proton gradient across the thylakoid membrane is the synthesis of ATP by ATP synthase.

During the light-dependent reactions, as electrons are passed through the electron transport chain in the thylakoid membrane, protons (H⁺) are pumped from the stroma into the thylakoid lumen. This creates a proton gradient with a higher concentration of protons in the thylakoid lumen compared to the stroma. ATP synthase, an enzyme embedded in the thylakoid membrane, allows protons to flow back from the thylakoid lumen to the stroma. The energy released from the flow of protons down their concentration gradient is used by ATP synthase to catalyze the conversion of ADP and Pi into ATP.